This invention relates to a method and apparatus for applying a screed coat to a roof surface.
The method according to the invention is particularly important for use in the renovation of existing flat roofs that have become deficient, and in the following description special attention will be paid to this use of the method, but as will be realized by the man skilled in the art, the method may also be used in connection with the construction of new roofs, where this may be found to be a practical and economic proposition.
Though it is an elementary rule that a roof should always be built in such a manner as to allow the rainwater to run off completely when the rain stops, this rule has nevertheless been neglected to a large extent in modern building, especially in the case of houses erected from pre-fabricated elements. In the interest of rationalization by using elements of uniform height, it became a temptation to make roofs not only flat, but level, with no gradient towards drains and gutters. The confidence in the water resistance and durability of modern roofing materials, such as high grade bitumen felt, was so great that it was thought to be reasonable to disregard the normal requirement that there be a gradient sufficient to permit rainwater to run off completely without fail. This practice was even accepted by the building authorities.
However, experience has shown that such gradient-less roofs are extremely apt to deteriorate, often after a relatively short period of time, and that this may have disastrous consequences for the whole of the building. After some time the roof supporting structure is apt to subside, whereby cavities are formed in the surface of the roof. The water cannot run off from these cavities, and in certain climates these roofs are more or less under water all the year round. The roof covering will tend to crack in these cavities, whereby the water will leak into the roof supporting structure, which then begins to decompose. Wooden structures are attacked by rot and dry rot, steel structures by rust, and insulating materials loose their insulating power.
There exists therefore an imminent need for methods and means for renovating such roofs before deterioration has started, or at least before it has proceeded so far that complete re-building is required.